1. Field of the Invention
The present invention relates to a handover processing system in a mobile communication system using a gateway device to connect a public switched telephone network (PSTN) and an Internet protocol (IP) network with each other.
2. Description of the Related Art
In recent years, information communication services including sound and data communications have diversified with the increase in information communication needs and with the liberalization of communications. Such background increases the number of carriers entering into the communication service field and raises service competition among the carriers. Each new carrier is called a new common carrier (NCC) and provides a variety of services by using a technology such as a voice over Internet protocol (VoIP). VoIP is a technology to integrate a sound-based network and a data-based network by packetizing digital sound data to transmit it (for instance, refer to Jpn. Pat. Appln. KOKAI Publication No. 2004-56336).
In many case, the NCC is able to loan facilities, such as an exchange, at a default rate from a specified carrier that owns a subscriber line. And many of the NCCs construct their own exchange networks, for example, IP networks using their own resources. Additionally adding a PSTN of the specified carrier to this exchange network forms a communication system. To provide services to general users, these facilities are utilized complexly. The NCC, obtaining the loan of the subscriber line, has to pay a line rental fee to the specified carrier at a flat rate and a pay-as-you-go rate in response to the use. Thus, a communication resource to be rented is minimized by setting up a gateway device between the subscriber network and the PSTN and by flowing traffic on the side of the IP network.
Incidentally, position information about a radio terminal (information indicating a service area being present in a specific are) is managed by the specified carrier. Thereby, the position information of the radio terminal not known in the IP network, handover processing (processing to change base station with which radio terminal communicates, also refereed to as handoff) is matched with the movement of the radio terminal.
As mentioned above, the flow of traffic to the side of the IP network by setting the gateway device to decrease charging from a carrier network has been presented. In the mobile communication system; however, being impossible to utilize information about the specified carrier in performing the handover processing in the mobile communication system, a failure involving handover accompanied by the movement of the radio terminal occurs.